Waveguide amplitude modulator



Aug. 21, 1956 T. MILLER 2,760,162

WAVEGUIDE AMPLITUDE MODULATOR Filed April 18, 1952 Modulating WITNESSES:INVENTOR MWZW E fTTQRNEY Theodore Miller.

United tates Patent house Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application April 18, 1952, Serial No.282,962

3 Claims. (Cl. 332-51) My invention relates to waveguide amplitudemodulators, and particulary to a waveguide amplitude modulator having abroad frequency response.

It is known to modulate electromagnetic energy bein propagated in ahollow metallic waveguide by applying a magnetic field to a section ofthe waveguide containing a material having a transmission loss dependentupon the intensity of the magnetic field. However, losses caused by eddycurrents induced in the waveguide walls limit the frequency response ofsuch modulators to less than 1,000 cycles, While at the same timetending to heat the waveguide walls and load the wave energy source.

It is an object of my invention to provide an improved waveguideamplitude modulator having a broad frequency response.

It is another object of my invention to provide a Waveguide amplitudemodulator which is responsive to a wide range of modulation frequencies.

It is another object of my invention to provide an improved waveguidemodulator of the type in which a modulating signal varies the intensityof a magnetic field, and in which eddy current problems are obviated.

The features of my invention, which I consider novel, are set forth inthe appended claims. The invention, together with additional objects andadvantages thereof, will be understood from the following description ofa specific embodiment when read in connection with the accompanyingdrawing, in which the single figure is a schematic diagram showing apreferred embodiment of the invention.

In the drawing, two rectangular waveguide sections 11, 13 are showncoupled together by means of a dielectric waveguide section 15. The endsof the rectangular waveguide sections 11, 13 have tapered portions 17,19 forming a transition to circular waveguide portions 21, 23. Thedielectric waveguide section 15 has a pair of cylindrical portions 25,27 which are fitted inside the circular portions of the rectangularwaveguide sections 11, 13. The end portions 29, 31 of the dielectricwaveguide section are tapered to insure a low reflection match betweenthe dielectric and metallic waveguide sections. The center portion 33 ofthe dielectric waveguide section is in the form of a cylindrical rodhaving a small diameter. The center portion 33 of the dielectricWaveguide 15 is joined by a pair of tapered portions 35, 37 to thecylindrical portions 25, 27 which fit inside the circular portions 21,23 of the metallic waveguides.

Transitions from rectangular metallic waveguides to dielectricwaveguides of the type just described, and of other types applicable tomy invention are known in the art. Transmission efliciencies comparableto those of ordinary waveguide are obtainable with the types ofdielectric waveguides used in these transitions. For a detaileddiscussion of low-loss dielectric waveguides and transitions of typessuitable for use with my invention, reference is made to the articleentitled An Investiga- "ice .2 tion of Dielectric Rod as Waveguide, byC. H. Chandler, Journal of Applied Physics, December, 1949.

Referring again to the drawing, there is shown an electromagnet 39having acoil 4'1 wound on a powdered "iron core 43. The electromagnet 39is disposed around the center portion 33 of the dielectric waveguidesection 15 so that the powdered iron core 43 will interceptelectromagnetic energy being propagated along the dielectric waveguidesection. A source of bias, shown as a battery 45, is connected in seriesWith an impedance, shown as a resistor 47 between the terminals 49, 51of the electromagnet. The modulating signal is impressed across theresistor 47.

In operation, when the waveguide is being excited by energy of thecarrier frequency, most of the electromagnetic energy being propagatedby the dielectric waveguide section will exist outside its centerportion. A modulating signal applied to the electromagnet will vary theintensity of its magnetic field. Variations in the intensity of theelectromagnet field will cause like variations in the permeability ofthe powdered iron core, which in turn will absorb varying amounts of theelectromagnetic energy being propagated along the waveguide. Modulationof the carrier energy is thus accomplished.

With an arrangement such as that shown in the drawing, the modulatingmagnetic field is entirely separated from metallic waveguide sectionsand so no eddy currents are induced in the waveguide walls.Consequently, this type of modulator is much more efficient than thoseknown in the prior art, and it will respond to a wide range ofmodulation frequencies.

It will be apparent to those skilled in the art that other types ofwaveguide transitions could be used as well as the specific one shown inthe drawing. It will also be apparent that other types of core materialcould be used for the electromagnet. The only limiting factors are thatthe modulating magnetic field should be applied to a dielectricwaveguide section, so that no eddy current losses are involved; that thedielectric waveguide section be of a low-loss type; that the transitionbetween the metallic waveguide sections and the dielectric waveguidesection should be an efficient one; and that the core material be of atype which will absorb the high frequency electromagnetic energy inaccordance with the variations in intensity of the modulating magneticfield. It will further be apparent that various dispositions of theelectromagnet with relation to the dielectric Waveguide section could beutilized. The only limiting factor in this respect is that the corematerial be disposed to intercept a suitable portion of the highfrequency electromagnetic energy being propagated along the waveguide.The electromagnet should of course be appropriately based forsubstantially linear operation.

While I have shown my invention in only one form, it will be obvious tothose skilled in the art that it is not so limited but is susceptible ofvarious changes and modifications without departing from the spiritthereof.

I claim as my invention:

1. A high frequency modulator comprising a low-loss solid dielectricwaveguide section interposed between and properly matched to a pair ofhollow metallic waveguide sections, a ring of powdered iron materialdisposed in the path of Wave energy propagated by said solid dielectricsection, a winding associated with said powdered iron material, meansfor applying a bias potential to said winding, and means for applying amodulating voltage to said Winding.

2. A high frequency modulator comprising a lowloss solid dielectricwaveguide section, a ring of powdered iron material surrounding saidsection and disposed in 3 4 the path of Wave energy being propagated bysaid secsion loss of said material in accordance with a modulattion, andmeans for varying the transmission loss of ing signal.

said material in accordance with a modulating signal.

R fer n es C'ted in the file of this atent 3. A high frequency modulatorcomprising a low-loss e e c l p solid dielectric waveguide sectioninterposed between and 5 UNITED STATES PATENTS properly matched with apair of hollow metallic wave- 2,286,428 Mehler June 16, 1942 guidesections, powdered iron material disposed in the 2,483,818 Evans Oct. 4,1949 path of Wave energy being propagated by said solid di- 2,607,031Denis et a1. Aug. 12, 1952 electric section, and means for varying thetransmis- 2,610,250 Wheeler Sept. 9, 1952

